The invention relates to fiber web technology. More especially the invention relates to a nozzle of a device for contact-free support of fiber web.
As known from the prior art fiber web making processes typically comprise an assembly formed by a number of apparatuses arranged consecutively in the process line. A typical production and treatment line comprises a head box, a wire section and a press section as well as a subsequent drying section and a reel-up. The production and treatment line can further comprise other devices and sections for finishing the fiber web, for example, a sizer, a calender, and a coating section. The production and treatment line also comprises at least one slitter-winder for forming customer rolls as well as a roll packaging apparatus.
As is known in the prior art, in some applications of drying, or carrying, etc. of a fiber web, for example a paper or board web, a device is needed which is capable of correcting any factors that may be related to the run of the web in the transverse direction of the machine, such as wrinkles, folds, and instabilities of the web. One way to solve these problems is to produce a web curved in the transverse direction of the machine. In contact-free treatment of a web, this can be achieved by creating a curved carrier face for the air nozzles that are used. Airborne web drying is used, e.g., in various coating applications, in particular in applications in which both sides of the web are treated at the same time.
With regard to the prior art related to airborne web drying, reference is made to publication EP 0 507 218 A1, which describes a dryer section including a contact-free web reversing device having a curved form so that the web is turned in the middle of the reversing curve, i.e., corresponding to the middle area of the web, to a greater extent than in lateral areas of the web. Further, in the device, the blow pressures are selected to be higher in the middle area than toward edges areas, so that the web obtains a curved form in the cross direction of the machine. The curved form of the blow pressure profile can be provided either by a web reversing device that is accomplished with a curved form or by regulating the blow pressures accordingly.
In publication EP 0 548 419 A1 is disclosed a device including a nozzle part formed in a manner so as to be adjustable, by means of support adjustable bolts attached at each end and in the middle to a base frame and to the nozzle, in a curved position in the cross direction of the machine. In this known structure the nozzle is bendable against the base frame.
In publication EP 0 726 220 B1 is disclosed a method for contact-free treatment of a running web by air blowing, said method comprising the steps of blowing air to treat the web through a nozzle-carrier-face unit which comprises a carrier face and which is fastened to a stationary frame part with opposite side walls arranged in a direction transverse to the running direction of the web, said stationary frame part operating as an air supply chamber, and regulating the profile of said nozzle-carrier-face unit in the transverse direction by adjustably bending said nozzle-carrier-face unit to provide a curved form for said carrier face in the transverse direction, wherein said nozzle-carrier-face unit is adjustably bent while being situated inside said frame part between said opposite side walls and while being displaced relative to said side walls. A device for contact-free treatment of a running web, comprising at least one stationary frame part operating as an air supply chamber comprising opposite side walls, a nozzle-carrier-face unit comprising a carrier face, wherein the opposite side walls of said at least one frame part and said nozzle-carrier-face unit extend substantially in a direction transverse to the running direction of the web, means for coupling said nozzle-carrier-face unit to said at least one frame part, and means for adjustably deflecting said nozzle-carrier-face unit relative to said at least one stationary frame part to provide a curved form for said carrier face in the transverse direction, wherein said nozzle-carrier-face unit is situated inside said at least one stationary frame part between said opposite side walls such that the nozzle-carrier-face unit is displaceable within said at least one stationary frame part and relative to said walls, and said adjustably deflected nozzle-carrier-face unit is fastened to said side walls by means of said coupling means.
With further regard to the prior art, reference is made to publication EP 1218589 A1, in which is disclosed an airborne web-drying apparatus for drying a travelling coated fiber web, such as a paper or board web, which apparatus comprises a nozzle arrangement including: an overpressure nozzle extending across the web and having on both sides of the nozzle, i.e. on the entrance and exit sides of the nozzle as seen in the web travel direction, a nozzle orifice arrangement extending across the web and comprising one nozzle slot or a row of successive nozzle orifices extending across the web, and which nozzle orifice arrangements are arranged to blow drying air jets obliquely against each other, or which nozzle orifice arrangements are arranged to blow drying air jets which are guided against each other with the aid of curved Coanda-surfaces, and at least one direct impingement nozzle extending across the web, in which direct impingement nozzle a plurality of nozzle slots or nozzle orifices are formed for blowing drying air mainly perpendicularly against the web, wherein said direct impingement nozzle is combined with said overpressure nozzle on the exit side or on the entrance side thereof in order to form a nozzle assembly such that no discharge passage for discharging wet air is formed between said direct impingement nozzle and said overpressure nozzle; the apparatus comprises on each side of the web two or more of said nozzle assemblies spaced-apart from each other in the web travel direction, wherein the gap between two adjacent nozzle assemblies on each side of the web forms a discharge passage for discharging wet air; and the nozzle assemblies are arranged on opposite sides of the web so that opposite each discharge passage between two adjacent nozzle assemblies on one side of the web there is on the other side of the web a nozzle assembly.
In publication DE 202012005534 U1 is disclosed a variable air nozzle for treating a fiber web, having a plurality of longitudinally extending air chambers with longitudinal side walls, in which air supply holes are formed, and a covering slide, which has openings functioning with the air supply holes, wherein the air supply holes can be blocked by displacement of the slide.
Disadvantages of the prior art known arrangements are in some cases occurring mechanical uncertainties due to possibly used complicated structures and possible limitations in adjustment. In known arrangements of the prior art there has sometimes also been difficulties to simultaneously achieve optimal curvature adjustability combined with efficiency.